<!DOCTYPE html>
<html lang="zh-CN">
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
        <meta name="author" content="郜建林">
        <title></title>
        <style>
            #app{
                display: none;
                font-size: 100px;
                color: lightskyblue;    
            }
            
        </style>
    </head>
    <body>
        <button id="btn">点击有惊喜</button>
        <div id="app">让你点你就点?</div> 
    </body>
    <script>
        var app = document.getElementById("app");
        var btn = document.getElementById("btn");
        btn.onclick = function(){
            app.style.display = "block";  
        }
    </script>
</html>